Pulse producing assembly

ABSTRACT

1. An assembly for producing a pair of pressure pulse sequences which comprises two arrays each having A. A PLURALITY OF EXPLOSIVE ELEMENTS ARRANGED IN A STRAIGHT LINE, SAID EXPLOSIVE ELEMENTS BEING EQUALLY SPACED FROM EACH OTHER A DISTANCE AT LEAST SUFFICIENT TO PREVENT DETONATION FROM PROPAGATING BETWEEN SAID ELEMENTS BY INFLUENCE, B. DETONATION-TRANSMITTING MEANS CONNECTING THE SAID EXPLOSIVE ELEMENTS IN SEQUENCE AND BEING ADAPTED TO PROVIDE IDENTICAL TIME INTERVALS BETWEEN THE DETONATION OF SUCCESSIVE ELEMENTS, AND C. INITIATING MEANS IN INITIATING RELATIONSHIP WITH ONE TERMINAL EXPLOSIVE ELEMENT IN SAID STRAIGHT LINE, BOTH OF SAID ARRAYS HAVING THE SAME SPACING BETWEEN SAID EXPLOSIVE ELEMENTS AND ESSENTIALLY THE SAME NUMBER OF SAID EXPLOSIVE ELEMENTS, AND SAID DETONATION-TRANSMITTING MEANS PROVIDING THE SAME TIME INTERVAL BETWEEN THE DETONATION OF SUCCESSIVE ELEMENTS IN BOTH OF SAID ARRAYS, SAID ARRAYS BEING SO DISPOSED ONE TO THE OTHER 1. THAT THE STRAIGHT LINE FORMED BY THE FIRST ARRAY IS PARALLEL TO A LINE PARALLEL TO THE STRAIGHT LINE FORMED BY THE SECOND ARRAY AND THAT THE LINE FORMED BY THE FIRST ARRAY AND THE LINE FORMED BY THE SECOND ARRAY LIE ON OPPOSITE SIDES OF A PLANE PASSING BETWEEN THEM AND NORMAL TO THEM, AND 2. THAT SAID TERMINAL EXPLOSIVE ELEMENTS, ONE FROM EACH ARRAY, IN INITIATING RELATIONSHIP WITH SAID INITIATING MEANS ARE SUBSTANTIALLY EQUALLY SPACED FROM THE GEOMETRIC CENTER OF SAID ASSEMBLY.

Andrews et a1. Aug. 29, 1972 [54] PULSE PRODUCING ASSEMBLY [72] Inventors: Alday B. Andrews, Woodbury, N.J.;

David L. Coursen, Newark, Del.

[73] Assignee: E. I. du Pont de Nemours and Com- EXEMPLARY CLAIM 1. An assembly for producing a pair of pressure pulse sequences which comprises two arrays each having a. a plurality of explosive elements arranged in a pany, Wilmington, Del.

straight line, said explosive elements being equally spaced from each other a distance at least Filed: g- 1962 sufficient to prevent detonation from propagating between said elements by influence, [21] Appl' 2l9340 b. detonation-transmitting means connecting the said explosive elements in sequence and being [52] US. Cl. ..102/22, 102/DIG. 2, 18l/0.5 XC adapted to provide identical time intervals [51] Int. Cl. ..F42d l/04, F42d 3/06 between the detonation of successive elements, [58] Field of Search ..340/3, 7; 181/0.5; 102/7, 10, and

102/11, 20.24, 27 initiating means in initiating relationship with one terminal explosive element in said straight line, 5 References Cited both of said arrays having the same spacing between said explosive elements and essentially UNITED STATES PATENTS the same number of said explosive elements, and said detonation-transmitting means providing the same time interval between the detonation of successive elements in both of said arrays, said arrays 2,715,365 8/ 1955 Godchaux et al ..102/27 bein d g so ispose one to the other 2,721,617 10/1955 Piety ..102/21.6 X 1 that the Straight line formed b th f t y e lI'S array is Hawkins et X to a to the Straight line 2,755,878 7/1956 Simth ..l02/2l X formed by the Second may and that the line 2,775,940 l/ 1957 Klotz, Jr. ..lO2/23 formed by the first array and li formed b 2,790,388 8/1957 lO2/2l.6 the second array l on opposite sides of a plane l between them and nonnal to them and Primary Examiner-Verlin R. Pendegrass Attorney-Samuel S. Blight 2. that said terminal explosive elements, one from each array, in initiating relationship with said initiating means are substantially equally spaced from the geometric center of said assembly.

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INVENTORS ALDAY B. ANDREWS DAVID L. COURSEN ATTORNEY PATENIEBmses m2 SHEEF 3 0F 3 H68 FIG-9 FIG-IO FIGII FIGIZ M 1 CCCCCCLCG g 4blll INVENTORS ALDAY B. ANDREWS DAVID L. COURSEN 3 ATTORNEY PULSE PRODUCING ASSEMBLY This invention relates to an explosives assembly for producing a pair of pressure pulse sequences the sum of whose periods is predetermined.

The use of explosive charges to produce pressure pulses, or sonic pulses, in underwater operations is known. Explosives are desireable as sources of sound to be transmitted over long distances in the ocean because their energy output per unit of time is high. Explosives sound sources also are advantageous in underwater operations since the explosives can be placed conveniently in the ocean, even at great depths. A need recently has arisen for a sonic source which emits a coded signal for purposes of underwater communication, e.g., between a submerged vessel and an airor surface-craft. For such purposes, an explosive sound source having controllable signal characteristics would be highly desirable.

In accordance with the present invention, there is provided an assembly for producing a pair of pressure pulse sequences the sum of whose periods is predetermined, said assembly comprising two arrays each having (a) a plurality of explosive elements arranged in a straight line, said explosive elements being equally spaced from each other a distance at least sufficient to prevent detonation from propagating between said elements by influence, (b) detonation-transmitting means connecting said explosive elements in sequence and being adapted to provide identical time intervals between the detonation of successive elements, and (c) initiating means in initiating relationship with one terminal explosive element in said straight line, both of said arrays having the same spacing between said explosive elements and essentially the same number of explosive elements, and said detonation-transmitting means providing the same time interval between the detonation of successive elements in both of said arrays, said arrays being so disposed one to the other 1) that the straight line formed by a first array is parallel to a line parallel to the straight line formed by the second array and is not intersected by a line normal to the straight line formed by the second array, and (2) that said terminal explosive elements, one from each array, in initiating relationship with said initiating means, are substantially equally spaced from the geometric center of said assembly.

The two terminal explosive elements, one from each array, which lie nearest each other in the assembly can be spaced from each other or contiguous to each other. Whether or not these elements are spaced from each other and, if they are, the particular spacing between them, are factors which depend on various conditions, to be discussed hereinafter. If the two lines formed by the two arrays lie on the same line, the spacing between the two nearest terminal elements is longitudinal and a line joining these two elements lies on the same line as the lines formed by the arrays. If the lines formed by the arrays lie on parallel lines, the spacing between the two nearest terminal elements is longitudinal and transverse, and a line joining these two elements will form an angle between 90 and 180 with the lines formed by the arrays.

In the most practical cases, there will be a spacing between the two terminal explosive elements, one from each array, which lie nearest each other, and this spacing generally will be within the range of (a) a distance substantially equal to the distance between explosive elements in each array to (b) a distance equal to twice the length of one of the arrays.

The geometric center of the assembly refers to (a) the midpoint of the line joining the two terminal elements, one from each array, which lie nearest each other in the assembly when these two elements are noncontiguous to each other, or (b) a point on the contiguous surfaces of these two terminal elements. This meaning is intended for assemblies wherein each array has exactly the same number of equally spaced explosive elements, as well as for assemblies wherein there is a slight disparity between the number of explosive elements in one array and in the other. In the latter case, the terminal explosive elements farthest from each other in the two-array assembly will not be exactly equally spaced from the geometric center, but substantially so. i

The term explosive element as used herein denotes a point charge which may be a finite segment of a linear charge. For example, the array of explosive elements may be comprised of a series of aligned point charges connected in sequence by a detonation-transmitting means; or the array may be comprised of a linear charge uniformly coiled or bent, e. g., in the form of a zig-zag or a helix, so that finite segments of the linear charge in the bends or turns are equally spaced apart in a straight-line arrangement, the segments in any straight line forming explosive elements and being connected in sequence by the portions of the linear charge between the aligned segments.

By terminal explosive element is meant the explosive charge at an end of a straight line of point charges, or the finite segment of a helical explosive charge which is the end segment in a straight line of segments.

In a linear array of spaced explosive elements, each explosive element is the center of a pressure front, and a pressure gauge placed at any selected position from such an array will register the arrival of pressure from successive elements as a succession of pressure pulses, the time interval between the arrival of the successive pulses, or the period of the pulse sequence, depending on the spacing between explosive elements and the time interval between detonation of successive elements. Because of the axial displacement of the centers of the pressure fronts, each array is a Doppler sound source, i.e., the time interval between the arrival of successive pulses, or the period of the pulse sequence, varies according to the angle between the receiver and the longitudinal axis of the array. In the present assembly, the two arrays of explosive elements have the same spacing between explosive elements and the same interval between detonation of successive elements. As a result, there is the same spacing between pulse fronts emanating in a normal direction from the two arrays, i.e., the period of the pulse sequence emanating normal from both arrays is the same. The period T of the pulse sequence emanating at any other angle from such an array is given by:

T= T +(d/C)cos 4),

where T is the period of the pulse sequence emanating in a normal direction from the array, d is the spacing between explosive elements, C is the sound velocity in the medium, and 4) is the angle between the direction from the array to the observer and the longitudinal axis of the array.

However, in the present assembly the initiated terminal explosive elements are substantially equally spaced from the geometric center of the assembly. This means that the two arrays are initiated at opposite ends relative to the center so that the axial displacement of pulse centers is in opposite directions in the arrays, i.e., there are two parallel detonation trains travelling in pposite directions with respect to each other. At any observation point from the assembly, two pulse sequences a and b are received having periods T,, and T,,, respectively. When the observation point is normal to the axes of the arrays, T and T,, are each equal to T At other angles from the arrays, the period of the pulse sequence a emitted by charge elements initiated in a sequence travelling in a direction away from the observer is T T (d/C) cos and the period of the pulse sequence 17 emitted by charge elements initiated in a sequence travelling in an opposite direction from the initiation sequence producing a and parallel thereto is T T (d/C) cos l 80) T (d/C) cos Adding the two periods:

T T,, T (d/C) cos 5 T (d/C) cos 4). Since d, C, and (ii are constant, T T,, 2 T,

Thus, although the period of each pulse sequence varies according to the angle between the receiver and the axis of the array, the sum of the periods of the two sequences is not angular-dependent and will be the same regardless of the observation point, i.e., the sum of the two periods received will be twice the period of the pulse sequence emanating normal from the arrays. The frequency or period of the pulse sequence emanating normal from the arrays as well as at other angles therefrom is determined by the distance between explosive elements and the time required for the detonation to be transmitted between elements and therefore is a controllable factor. Consequently, the assembly of this invention produces pulse sequences which, by virtue of having a predetermined frequency characteristic independent of the location of their reception point relative to their emission point, can be used to great advantage as a code or signal together with suitable identifying means in underwater operations. Specific methods of use will be described hereinafter.

In order to describe the invention more fully, reference is now made to the accompanying drawings in which:

FIGS. 1 and 2 show schematically the pattern of pulses emanating from each of two arrays of nine equallyspaced explosive elements forming a straight line and detonating at equal time intervals, each figure showing three rays traversing different pulse paths from the array;

FIGS. 1A and 2A show a series of pulse points along each of the three different paths in the pulse patterns shown in FIGS. 1 and 2, respectively;

FIG. 3 shows schematically the pattern of pulses emanating from an assembly comprising the two arrays of FIGS. 1 and 2 positioned so that all of the explosive elements lie on the same straight line, and so that the initiated terminal elements of the arrays are adjacent elements in the assembly and are spaced from each other a distance equal to the distance between other elements in the assembly;

FIG. 3A shows the addition of the spacings between pulse points along a pair of paths emanating at the same angle from the two arrays of the assembly of FIG. 3;

FIG. 4 is an embodiment of the explosives assembly of this invention wherein the two arrays of explosive elements are aligned point charges and the charges to be initiated first are those closest to each other in the two-array assembly;

FIG. 5 is an embodiment of the explosives assembly wherein the arrays of explosive elements are helical explosive charges initiated at the furthermost ends thereof in the two-array assembly;

FIG. 6 is an embodiment of the explosives assembly wherein the arrays of explosive elements are formed from one helical explosive charge initiated at essentially its midpoint;

FIG. 7 shows an explosives assembly of two arrays of point charges, wherein the charges initiated are those furthermost from each other in the two-array assembly and wherein the initiation of the arrays is non-simultaneous;

FIG. 8 shows an explosives assembly of two helical charges in non-axial alignment and initiated at the furthermost ends thereof in the two-array assembly;

FIG. 9 shows an assemblage of two-array assemblies, each assembly comprising two helical charges of the same uniform diameter and pitch, and the diameter of the helical charges varying from one assembly to another;

FIG. 10 shows an assemblage of two-array assem-' blies, each assembly being formed from one helical explosive charge of uniform diameter and pitch, and the diameter of the helical charges varying from one assembly to another;

FIG. 11 shows the assembly depicted in FIG. 6 connected to a series of helical charges of different diameters; and

FIG. 12 shows the assembly depicted in FIG. 6 connected to a series of helical charges positioned at different angles to an extension of the longitudinal axis of the said assembly.

Referring now to the drawings in greater detail, in FIG. 1, E represents an array of nine equally spaced explosive elements connected in sequence by a detonation-transmitting means (not shown) which provides identical time intervals between the detonation of successive elements. Initiation of the array takes place at the terminal explosive element labelled I. Detonation travels at constant velocity through the detonationtransmitting means connecting the elements. The pressure fronts, moving at constant velocity radially from the explosive elements producing them, describe a series of nine circles having centers at each of the nine elements, the circle whose center is I having the longest radius and each of the circles with centers at the next consecutive elements being consecutively shorter in radius than the immediately preceding circle by a constant decrement owing to the constant time interval between the detonation of each element. Because of the shift in the centers of the pressure fronts, the

distance between fronts is at a minimum in the direction in which the detonation progresses, and increases to a maximum in the opposite direction. Consequently, three rays A, N, and B, which leave the array at different angles therefrom, have different frequencies or periods. A, which is emitted at an angle between the normal and the direction of detonation travel, has a higher frequency and shorter period than N, which is emitted normal to the axis of the array; and N has a higher frequency and shorter period than B, which is emitted in the direction away from which detonation travels.

FIG. 1A illustrates the pulse pattern produced along paths traversed by rays A, N, and B as it would be recorded by a pressure-pulse recorder.

In FIG. 2, E is an array identical to array E of FIG. 1. Initiation of array E takes place at element I. Ray A leaves array E at the same angle as ray A leaves array E of FIG. 1-. However, A is emitted at an angle between the normal and the direction away from the detonation travel. N is emitted normal to the axis of array E. B is emitted in the axial direction of detonation travel. Consequently, the period of A is longer than that of N, which in turn has a longer period than B.

FIG. 2A illustrates the pulse pattern produced along paths traversed by rays A, N, and B as it would be recorded by a pressure-pulse recorder.

In FIG. 3, arrays E and E from FIGS. 1 and 2, respectively, are shown positioned in axial alignment to form a typical assembly of the instant invention, elements I and I at which initiation of the arrays occurs being the two elements, one from each array, nearest each other. In FIGS. 1, 2, and 3, the pulse fronts from E are shown as circles drawn with solid lines, and pulse fronts from E as circles drawn with broken lines. Because the spacing between elements and arrays, and consequently the spacing between rays emitted from the assembly at the same angle, e.g., A and A, is negligible with respect to the the much greater distance between the assembly and a receiver, a receiver R will receive two pulse sequences, i.e., pulse sequences produced along paths traversed by A and A. In like manner, a receiver in the path of N and N will receive both sequences, and a receiver in an axial path from the assembly will receive sequences B and B. It is seen from FIGS. 1A, 2A, and 3A that the spacing. between pulses along paths traversed by N and N are equal; that the spacings between pulses along paths traversed by A and A add up to twice the spacings between pulses along paths traversed by N (A A 2 N); and that the spacings between pulses along paths traversed by B and B add up to twice the spacings between puls'es along paths traversed by N (B B 2 N). Similarly, if one or a pair of parallel lines is drawn from any angle from the assembly, the line or lines will connect two pulse sequences whose spacings add up to twice the spacing between pulse fronts in paths traversed by N or N.

In the assemblies of FIGS. 4 and 7, la represents explosive charges in one array and lb explosive charges in a second array, the spacing between any two la charges being the same as the spacing between any two lb charges, and all of the charges in the assembly being in axial alignment and spaced from each other a distance sufficient to prevent detonation of one charge by the detonation of another charge by influence. The charges in each array are connected in sequence by a length of detonating cord 2 which detonates at a uniform velocity, the length of detonating cord 2 between charges being equal in all cases. In FIG. 4, an initiator 3 is affixed to terminal charges 1a and lb closest to each other in the assembly, e. g., via a section of the detonating cord 2. In the assembly of FIG. 7, an initiator 3 is affixed to charge 1a furthermost from the other array of charges, and charge la most remote from initiator 3 is connected to charge lb most remote from said initiator by means of detonating cord 2.

The assemblies of FIGS. 5 and 8 are comprised of helical explosive charges 4a and 4b in spaced relationship to each other and having the same uniform pitch and diameter, and the same number of turns. 40 and 4b are constructed from a linear explosive having the same uniform detonation velocity, helixes 4a and 4b having initiators 3a and 3b, respectively, affixed to their furtherrnost ends in the assembly. In the assembly of FIG. 5, the helical axes of 4a and 4b are in alignment and the charges are held in spaced relationship toeach other by holding member 5, e.g., a rigid rod. In the assembly of FIG. 8, helical charges 4a and 4b are non-axially aligned, the axis of one helix being parallel to an extension of the axis of the other helix. In FIG. 8, the charges are shown on a support 6, e.g., a piece of wood or metal, on which they are fixed in their proper positions, e.g., by taping.

The assembly depicted in FIG. 6 is comprised of one helical explosive charge of uniform pitch and diameter and constructed from a linear explosive having a uniform detonation velocity. An initiator 3 is affixed at the midpoint of the linear explosive, thus in effect forming an assembly of two identical helical explosive charges 4a and 4b joined together by the linear explosive itself, the initiator initiating the terminal elements, one in each helical charge, adjacent to the midpoint of the linear explosive.

In the assembly shown in FIG. 9, an explosives assembly like that depicted in FIG. 6, except that helical charges 40 and 4b are wound in opposite directions, is the starting unit of the composite assembly, or the explosive unit at which the initiation of the assembly by initiator 3 originates. Helical charges 40 and 4b are connected in sequence to helical charges 4a 4a and 4a and 4b 4b and 4b respectively; charges 4a and 4b, 4a and 4b, 4a" and 4b, and 4a and 4b, are pairs of helical charges, both members of the pair having the same uniform diameter and pitch and the same number of helical turns, and each pair of charges having a different diameter than the other pairs. In this assembly, the b charges are wound opposite to the a charges.

In the assembly of FIG. 10, an explosives assembly like that depicted in FIG. 6 again is the starting unit of the composite assembly, helical charge 4b being connected to the midpoint of the linear explosive forming the array of 4a-4b helical charges; charge 4b is similarly connected to the next unit, 4a"-4b, and charge 4b similarly connected to the next unit, 4a 4b. Each pair of charges in a unit has a difierent diameter than pairs of charges in other units.

In FIG. 1 l, helical charge 4b of the assembly 4a4b is connected in sequence to helical charges 4, 4", and 4", each of different diameter.

In FIG. 12, helical charge 4b of the unit 4a 4b is connected in sequence to a series of helical charges 4, all having the same diameter and arranged so that their axes form different angles with an extension of the longitudinal axis of unit la-$1).

In operation of the assembly of FIG. 4, actuation of initiator 3 causes a detonation impulse to arrive at adjacent charges la and lb simultaneously and thereafter to the remaining charges in both arrays; corresponding charges in each array, taken from the point of initiation, being detonated at essentially the same time as a result of the equal length of detonating cord of uniform detonation velocity connecting the charges. Therefore, the pattern of pulses emanating from this assembly resembles that depicted in FIG. 3, the detonation trains in the two arrays travelling away from each other.

In the assembly of FIG. 7, the two arrays are initiated non-simultaneously, initiator 3 initiating the adjacent charge la and the detonation travelling through all changes Ia before the array of lb charges is initiated. Charge lb most remote form initiator 3 is initiated by the detonation impulse from the last charge 10 and transmitted via detonating cord 2. Whereas in the operation of the assembly of FIG. 4, two detonation trains travel simultaneously in opposite directions away from the center of the assembly, in the assembly of FIG. 7 two detonation trains travel non-simultaneously in opposite directions from the two ends of the assembly toward the center thereof.

The assembly of FIG. 6 operates like that of FIG. 4, actuation of initiator 3 resulting in two detonation trains travelling simultaneously in opposite directions away from the center of the assembly.

The assemblies of FIGS. and 8 produce two detonation trains travelling simultaneously toward each other from the two ends of the assembly owing to simultaneous initiation of arrays 4a and 4b by initiators 3a and 3b at their furthermost ends, the horizontal separation between arrays 4a and 4b in the assembly of FIG. 8 having no effect on the summation of the periods of the pulse sequences received at a distance therefrom.

When the assembly shown in FIG. 9 is in operation, actuation of initiator 3 produces two detonation trains travelling simultaneously in opposite directions from the midpoint of the assembly. Each pair of helixes in a two-array unit is initiated simultaneously, i.e., helical charge 40 and 4b by initiator 3, charges 4a and 4b by charges 40 and 4b respectively, and so forth. A pressure-pulse receiver will receive pairs of pulse sequences the sum of whose periods will change with time owing to the difference in diameter of the pairs of helixes 4a-4ba, 4a 4b, 4a"4i-b", and 4a"'-4b". A receiver also will receive pairs of pulse sequences the sum of whose periods will change with time when the assembly of FIG. 10 is in operation. However, in this case, after initiation of arrays in and 41; by initiator 3, the initiation of the two helical charges in each subsequent unit is effected by connection of the end of a charge in the previous unit with the midpoint of the unit to be initiated.

In the assemblies depicted in FIGS. 11 and 12, the 411-417 unit operates like the assembly of FIG. 6. After the detonation has travelled through helical charges In and 4b simultaneously, it proceeds consecutively through a number of helical charges of varying diameter (FIG. II) or positioned at varying angles to an extension of the longitudinal axis of the la-4b unit (FIG. 12). Each of these helical charges is initiated only at one end and therefore the pressure pulses produced therefrom will be received as a single pulse sequence, the period of which varies according to the angle of observation, as described previously. When the helical charges have different diameters or are disposed at different angles in the assembly, the pulse sequence received at any angle from one helical charge will be different from that received at the same angle from a different helical charge in the assembly.

The assembly of this invention can be used together with appropriate receiving and detecting apparatus in a triggering system. For example, if it is desired to trigger a mechanism under the surface of the water on command from the surface, the assembly, e.g., any of those depicted in FIGS. 4 through 8, can be dropped from a surface vessel or an aircraft, and the pulse sequences produced on initiation of the charges will be received and detected automatically by an apparatus which, on reception of the proper signal, produces an electrical signal to put the mechanism in operation as desired. A signal-detecting circuit which may be used to recognize the signals from the two-array assembly of this invention is disclosed in co-pending application, Ser. No. 219,341 filed Aug. 24, 1962.

The assembly of this invention, as depicted, for example, in FIGS. 4 through 12, can also be used in a system for communicating between a surface or aircraft and submerged submarines. The number of pairs of pulse sequences produced, i.e., the number of twoarray units in the assembly, or the number of single pulse-sequences produced in addition to the initial pair of pulse sequences, depends on the length and type of message which one desires to communicate. Assemblies such as those depicted in FIGS. 9 through 12 are able to provide multi-symbol messages. The signals are received by a hydrophone, and the electrical impulses emitted by the hydrophone are either used to furnish a visual record for decoding by personnel on the submarine, or the signals are detected automatically, for example, by use of the circuit disclosed in the abovementioned copending application.

It has been pointed out that in the assemblies of FIGS. ll and 12, the period of the single pulse sequence received from the helical charge initiated at only one end will vary according to the angle of observation. It will be possible, however, to recognize the message sent owing to the fact that the angle of observation can be calculated from a knowledge of the difference in the periods of the two pulse sequences received from the center-initiated helix. This calculation is made by subtracting the equation for one period from that for the other:

T,,= T (d/C) cos d) The last equation can be solved for (b by substituting the values of T and T found by visual record. A preferred method for determining is to employ the sorting circuit disclosed in co-pending application, Ser. No. 219,342 filed Aug. 24, 1962. Since the period expected at different angles from the single helical charge is known, the period emitted by the charge at known (I) will be determined and the message recognized.

As is shown in FIG. 3, the pressure pulse fronts from the two arrays must be equally spaced from each other in opposite directions from the geometric center of the assembly. Stated in another manner, when one array is superimposed upon the other (e.g., array E of FIG. 1 upon array E of FIG. 2), with initiated elements coinciding, the pulse fronts, or circles, from the two arrays coincide. This condition must be met if both arrays are to have the same normal period and if the two pulse sequences emanating at any one angle from the twoarray assembly are to have periods totalling twice this normal period. To meet this condition, the aligned explosive elements in both arrays must be equally spaced from each other, this spacing being sufficient to prevent detonation of an explosive element by detonation of an adjacent aligned element by influence. In addition, the time between the detonations of explosive elements must be the same in both arrays.

The particular spacing and time delay between successive explosive elements in the two arrays, and therefore the periods of the pulse sequences emanating in all directions from the arrays, will be selected on the basis of several factors. Obviously, the periods chosen should be those which propagate well in the ocean, and also, if possible, in a range for which there is a minimum of interference from sounds normally encountered in the ocean. Further, the time interval between the detonation of successive aligned explosive elements in the two arrays must be such as to provide an axial component of the detonation velocity, i.e., an effective velocity of detonation in the direction of travel of the detonation, of less than the speed of sound in the surrounding medium, i.e., less than 1,500 meters per second fro underwater operations. If the axial component of the detonation velocity equals the speed of sound in the surrounding medium, the pulses emitted from each explosive element will superimpose in an axial direction from the array to form a single pulse. If the axial component of the detonation velocity exceeds the speed of sound in the medium, there will always exist certain directions from the array where the pulses will superimpose to form a single pulse. In general, for underwater communications purposes, the time interval between pulses, or the period of the pulse sequence, may range from about 0.02 millisecond to about 2 milliseconds.

Obviously, in order to produce pulse sequences, there must be at least two aligned explosive elements in each array. Beyond this, the particular number of such elements in each array is not critical to the invention. Generally, however, for discrimination of the signals from interfering noises, it is preferred to have more than two, e.g., at least about five, aligned explosive elements in each array. The maximum number of elements which will be used will depend on such factors as case of construction and handling, length of pulse sequence desired, etc. Arrays each having as many as 1,000 aligned explosive elements or more may be used.

Generally, the number of aligned explosive elements in one array will be approximately equal to the number of such elements in the other array. A slight disparity in the number of explosive elements in the two arrays will not be deleterious, particularly with arrays having a large number of such elements, since only a slight difference in the lengths of the two pulse sequences will result. In an array of two helical charges having the same number of turns, the obtaining of the same number of pulses from each array at any specified direction from the array requires that the starting points for the windings in both helixes lie in a straight line along the length of the cylinder formed by the helixes. It is not necessary that the starting points of the windings be so disposed. Further, in an assembly of two helical charges, the helixes may be wound in opposite directions provided that the helixes have the same pitch and diameter, i.e., the same time delay between detonation of successive aligned segments.

In order to provide pulse sequences having a preselected normal period, the arrays of explosive elements are connected in sequence by a detonationtransmitting means providing a time interval between detonation of successive elements equal to the preselected normal period. The particular detonationtransmitting means employed between point charges must be one which provides a uniform time delay between the detonation of the successive charges in both arrays. One may use a length of a detonating cord such as Primacord or the low-energy connecting cord described in U.S. Pat. No. 2,982,210. Such cords propagate detonation at a uniform velocity of approximately 7,000 meters per second. By selection of an appropriate length of such a cord, a precise time interval between detonation of successive elements, and therefore between sequential pulses, can be obtained. The low-energy connecting cord is a preferred cord because it has low brisance and can be tightly coiled or folded without danger of cut-off or short-cutting of the detonation. To insure initiation of the cord and of the point charges, an initiator or booster may be fastened to each end of the cord. Alternative delay devices, such as electric delay caps, may be used between charges provided the accuracy of delay is adequate to provide the necessary precise time interval between pulses. In the case of an array of two helical charges, the linear explosive forming the helical charge acts itself as the detonation-transmitting means between aligned explosive elements. Therefore, to provide the constant time interval between detonations, it is necessary that both helical charges be made from a linear explosive charge which detonates at the same uniform velocity, and that both have the same diameter and pitch, i.e., that the length of the linear charge between aligned elements is the same in both helixes.

The explosive charges in the arrays may be made from any detonating explosive which will detonate reliably, when submerged, at a velocity in the range of 1,700 to 10,000 meters per second. For ease in han dling and assembling, the charges preferably will be made of a self-supporting explosive composition, for example cast TNT compositions or compositions of the type described in U.S. Pat. Nos. 2,992,087 and 2,999,743. The latter compositions are water-insensitive and can be worked into various forms, for example into a cylindrical form to produce a series of cylindrical point charges. Or they may be extruded into a self-supporting cord or tape, which may be wrapped or bent in the form of a helix or zig-zag. A detonating cord such as Primacord also may be used to form the helical charges.

The respective positions of the two arrays in the explosives assembly of this invention is a critical factor to the proper functioning of the assembly. The arrays ill must be so disposed one to the other that the two straight lines formed by the two arrays of explosive elements are parallel to the same line and that the line formed by one array is not intersected by a line normal to the line formed by the second array. The two terminal elements, one from each array, lying nearest to each other in the assembly can be contiguous or spaced from each other. The two lines formed by the two arrays may lie on the same line (FIGS. 4-7) or they may lie on parallel lines (FIG. 8). Thus, there may be a longitudinal spacing or a longitudinal as well as transverse spacing between the two terminal elements, one from each array, lying nearest to each other in the assembly. This spacing has no adverse effect on the proper functioning of the assembly provided that the necessary Parallelism is maintained and that the lines in the two arrays lie on opposite sides of a plane or pair of parallel planes between them and normal to them. That such variations still provide an assembly having the desired property of period summation can be seen by placing FIG. 1 over FIG. 2 in such a manner as to maintain these restrictions but at the same time varying the spacings between E and E. It is seen that no change occurs in the direction of the pulse paths shown.

The particular spacing, if any, between the nearest terminal elements, one from each array, in the assembly depends on various factors including the type of explosive charges used, relative ease of assembling, relative positioning of the assembly and the detector, etc. While no spacing is necessary between the nearest terminal elements, one from each array, it may be more convenient from the point of view of assembling and maintaining position if there is a spacing between these elements. Generally, there is no advantage to having a longitudinal spacing between the arrays of the assembly beyond a spacing comparable to that between any two explosive elements in the arrays. If desired, however, greater longitudinal spacings may be used, although generally such spacings will not be much greater than twice the length of one of the arrays. When several twoarray assemblies of differing total periods are used, such as the assembly shown in FIG. 9, it will be understood that it will be necessary to have increasingly greater longitudinal spacings between the two arrays of each pair as the pair becomes farther removed from the initial assembly, e.g., increasingly greater spacings between charges 4a and 4b, 4a" and 4b", and 4a and 4b" The transverse spacing between arrays, i.e., the spacing between the parallel lines on which the straight lines of explosive elements lie, may be as large as handling and launching difficulties will permit. However, an assembly having a large transverse spacing between arrays generally will not be used because of difficulties associated with packaging such an assembly, or with maintaining widely separated arrays in their necessary respective positions. A practical maximum transverse spacing is about twice the length of one of the arrays.

As is shown in FIG. 6, the two-array assembly may be fashioned from a single array of explosive elements, or, in this case, a single helical charge. A continuous line of point charges with interconnecting detonation trans mitting means also may be used. In such single arrays, the explosive element at the approximate midpoint of the array may be considered to be an explosive element between two arrays and may be the point of initiation for the two arrays. The single-array construction may be desirable from the point of view of ease of fabrication; but such a construction may be unwieldy and it may be preferable to make the assembly from two arrays, or from more than two arrays suitably joined together to produce the two-array assembly.

Each array in the assembly of the invention is initiated at a terminal explosive element'therein, the two initiated elements in the assembly, one from each array, being substantially equally spaced from the geometric center of the assembly. This means that the arrays are initiated at opposite ends, i.e., at the two closest terminal explosive elements in the linear series in the arrays, or at the furthermost explosive elements therein, so that the detonations travel through the two arrays in opposite directions. For example, an initiator may be placed in initiating relationship to the center charge of a series of point charges, or to the midpoint of a linear charge arrayed in the form of a helix. In units wherein there is longitudinal and/or horizontal separation between the arrays, an initiator may be placed in initiating relationship to both of the two closest charges or charge segments; or each of said charges or seg ments may have its own initiator affixed to it. Initiation of the furthermost elements in the unit may be efiected as shown in FIGS. 5 and The two arrays may be initiated simultaneously or non-simultaneously. For example, a convenient arrangement is to initiate one array by the detonation impulse provided by the detonation impulse provided by the detonation of the last explosive element in the other array. Thus, the delay between initiations of the two arrays may be the length of time it takes for detonation to travel through one array plus the time required for the detonation impulse to arrive at the explosive element in the second array to be initiated. While the particular time interval employed between initiation of the two arrays will depend on such factors as the time interval between successive pulses in the pulse sequences produced, the longitudinal spacing between arrays, etc., in general this time interval will vary from zero to the time required for the sonic pulse from the explosive element detonating last in the first array to reach the first element of the second array. The initiator or initiators used are conventional and may be actuated by a timing device or by the pressure of the water at a selected depth. One of the suitable initiators which can be used is the pressure-actuated detonator described in U.S. Pat. No. 2,726,602.

The particular means used to join arrays and to hold them in their required positions, as well as the means used to package the arrays, e.g., for underwater use, are not critical to the functioning of the units or assemblies of this invention, provided that the means used maintain the necessary spacing of explosive elements during the uninterrupted travel of the detonations through the linear series of elements. Obviously, in order to maintain pitch, diameter, and orientation of the arrays and array elements relative to each other, the units and assemblies depicted in all the figures require a support or holding member. Spacing between elements can be maintained, for example, by stringing point charges on a rigid support; or by afiixing a linear charge to a wire of spring steel in helical form having the necessary diameter and pitch, and attaching rigid spacer elements to the spring steel between turns.

The constructing of the assemblies shown in FIGS. 9 through 12 can be effected by forming the helixes from one length of explosive by winding in different diameters, or by joining helixes wound from different lengths of explosive. The assemblies will be maintained on a suitable support, e.g., a central rod therethrough to which the helical charges are affixed.

Obviously, if the explosives and/or the initiators used are adversely affected by water, a waterproof container will be provided for them. Also, the assemblies may be provided with weights, guide vanes, and/or nose cones to facilitate their fall through the air or the water.

The invention has been described in detail in the foregoing. Many modifications and alterations will be apparent to those skilled in the art and will not require departure form the spirit of this invention. Accordingly, it is intended that the invention be limited only by the following claims.

What is claimed is:

1. An assembly for producing a pair of pressure pulse sequences which comprises two arrays each having a. a plurality of explosive elements arranged in a straight line, said explosive elements being equally spaced from each other a distance at least sufficient to prevent detonation from propagating between said elements by influence,

. detonation-transmitting means connecting the said explosive elements in sequence and being adapted to provide identical time intervals between the detonation of successive elements, and

c. initiating means in initiating relationship with one terminal explosive element in said straight line, both of said arrays having the same spacing between said explosive elements and essentially the same number of said explosive elements, and said detonation-transmitting means providing the same time interval between the detonation of successive elements in both of said arrays, said arrays being so disposed one to the other 1. that the straight line formed by the first array is parallel to a line parallel to the straight line formed by the second array and that the line formed by the first array and the line formed by the second array lie on opposite sides of a plane passing between them and normal to them, and 2. that said terminal explosive elements, one from each array, in initiating relationship with said initiating means are substantially equally spaced from the geometric center of said assembly.

2. An assembly according to claim 1, wherein an explosive element is located at the mid-point of a line joining the two terminal explosive elements, one from each array, which lie nearest each other.

3. An assembly according to claim 1, wherein the straight lines formed by the two arrays lie on the same line.

4. An assembly according to claim 1, wherein said initiating means are in initiating relationship with the two terminal explosive elements, one from each array, which lie nearest each other.

5. An assembly according to claim 1, wherein said initiating means are in initiating relationship with the two terminal explosive elements, one from each array,

which lie farth t f om ea h other.

6. An assem y or pro ucmg a pair of pressure pulse sequences which comprises two arrays each having a. a length of explosive arranged in the form of a helix, the helixes in the two arrays'having approximately the same number of turns and the same uniform pitch and diameter, the explosive and the distance between helical turns being such as to permit continuous propagation of detonation throughout all the turns at constant velocity, and initiating means in initiating relationship to a terminal segment of said length of explosive in each array, said arrays being so disposed one to the other 1. that the straight line formed by aligned segments of the helix of the first array is parallel to a line parallel to the straight line formed by aligned segments of the helix of the second array and that said two straight lines lie on opposite sides of a plane passing between them and normal to them, and

2. that said terminal segments, one from each array, in initiating relationship with said initiating means are substantially equally spaced from the geometric center of said assembly.

7. An assembly according to claim 6, wherein the said arrays are formed from one continuous length of explosive arranged in the form of a helix, and said initiating means is afiixed to essentially the midpoint of said length of explosive.

8. An assembly according to claim 1, wherein the initiating means in initiating relationship to a terminal explosive element in one of said arrays is a length of detonating cord which connects said element to the terminal explosive element of the other array which detonates last.

9. A composite assembly for producing pairs of pressure pulse sequences which comprises a plurality of the assemblies of claim 1, wherein the time for detonation to be transmitted between any two successive aligned elements in the two arrays in one assembly differs from the time for detonation to be transmitted between successive aligned elements in other assemblies, said assemblies being so disposed that initiation of one assembly takes place only after detonation has travelled completely throughout a previously initiated assembly.

10. The assembly of claim 1 in combination with Doppler explosive charges. 

1. An assembly for producing a pair of pressure pulse sequences which comprises two arrays each having a. a plurality of explosive elements arranged in a straight line, said explosive elements being equally spaced from each other a distance at least sufficient to prevent detonation from propagating between said elements by influence, b. detonation-transmitting means connecting the said explosive elements in sequence and being adapted to provide identical time intervals between the detonation of successive elements, and c. initiating means in initiating relationship with one terminal explosive element in said straight line, both of said arrays having the same spacing between said explosive elements and essentially the same number of said explosive elements, and said detonation-transmitting means providing the same time interval between the detonation of successive elements in both of said arrays, said arrays being so disposed one to the other
 1. that the straight line formed by the first array is parallel to a line parallel to the straight line formed by the second array and that the line formed by the first array and the line formed by the second array lie on opposite sides of a plane passing between them and normal to them, and
 2. that said terminal explosive elements, one from each array, in initiating relationship with said initiating means are substantially equally spaced from the geometric center of said assembly.
 2. that said terminal explosive elements, one from each array, in initiating relationship with said initiating means are substantially equally spaced from the geometric center of said assembly.
 2. An assembly according to claim 1, wherein an explosive element is located at the mid-point of a line joining the two terminal explosive elements, one from each array, which lie nearest each other.
 2. that said terminal segments, one from each array, in initiating relationship with said initiating means are substantially equally spaced from the geometric center of said assembly.
 3. An assembly according to claim 1, wherein the straight lines formed by the two arrays lie on the same line.
 4. An assembly according to claim 1, wherein said initiating means are in initiating relationship with the two terminal explosive elements, one from each array, which lie nearest each other.
 5. An assembly according to claim 1, wherein said initiating means are in initiating relationship with the two terminal explosive elements, one from each array, which lie farthest from each other.
 6. An assembly for producing a pair of pressure pulse seQuences which comprises two arrays each having a. a length of explosive arranged in the form of a helix, the helixes in the two arrays having approximately the same number of turns and the same uniform pitch and diameter, the explosive and the distance between helical turns being such as to permit continuous propagation of detonation throughout all the turns at constant velocity, and b. initiating means in initiating relationship to a terminal segment of said length of explosive in each array, said arrays being so disposed one to the other
 7. An assembly according to claim 6, wherein the said arrays are formed from one continuous length of explosive arranged in the form of a helix, and said initiating means is affixed to essentially the midpoint of said length of explosive.
 8. An assembly according to claim 1, wherein the initiating means in initiating relationship to a terminal explosive element in one of said arrays is a length of detonating cord which connects said element to the terminal explosive element of the other array which detonates last.
 9. A composite assembly for producing pairs of pressure pulse sequences which comprises a plurality of the assemblies of claim 1, wherein the time for detonation to be transmitted between any two successive aligned elements in the two arrays in one assembly differs from the time for detonation to be transmitted between successive aligned elements in other assemblies, said assemblies being so disposed that initiation of one assembly takes place only after detonation has travelled completely throughout a previously initiated assembly.
 10. The assembly of claim 1 in combination with Doppler explosive charges. 